1. Field of the Invention
The present invention relates to an image transmission system for transmitting and receiving image information.
2. Description of the Prior Art
As a system for transmitting image information between distant locations, there is already known a facsimile apparatus utilizing telephone lines.
Such known facsimile is however not yet satisfactory with respect to the resolving power or transmission speed. Also such facsimile is not adequate in terms of the installation and maintenance costs in order to respond to a requirement of image transmission within a limitcd area, such as within a determined building site.
Also an apparatus for receiving image information and reproducing an image, for example a printer, is usually shared by several persons because it is generally expensive and requires a relatively large space for installation, so that the transmitted information may be received regardless of the will of the addressee through the operation of another person even when the addressee is absent. Such unwanted transmission of the information can naturally be avoided if the transmission is effected only when the addressee is present, but for this purpose the sender of the information has to confirm the presence of the addressee at least once.
In an image transmission system with plural transmitting units, image transmission from a first unit to a second unit is effected only after a command signal emitted by the first unit is confirmed by the second unit. In such image transmission system, there may occur collision of information in the system in the case that demands for transmission are simultaneously emitted from plural units or in case a demand for transmission is emitted while image transmission is already going between other units of the system. In order to avoid such collision it has been necessary, therefore, to give priority ranking to the units or to circulate a particular signal, indicating that the transmission of information is under way, in the system.
Also such system is constructed in such a manner await the completion of reception, if an addressee unit is in the course of receiving image information from another unit, and to initiate the new image transmission after the operator of the sending unit confirms that the receiving unit has become available for receiving the new information.
Thus, the image transmission is apparently impossible if the receiving unit is not available for reception, even if the sending unit is available for sending. Stated differently, image transmission is possible only when both the sending unit and the receiving unit are available.
Also the transmission of image information from a unit to plural units may be achieved either by successively repeating transmission from a unit to each of the others in sequence or by simultaneous transmission to plural receiving units.
The former method involves a repetition of the transmission equal to the number of receiving units and consequently requires a considerable time for transmission when the number of receiving units is large.
On the other hand, in the latter method, the image transmission may be prohibited if all the units designated as addressees are not available for reception.
Also, with the progress of technology for handling image information in the form of electric signals, there have been proposed image processing apparatus incorporating two functions as copier and as facsimile.
Such apparatus with two functions usually has a priority ranking for the information to be processed so that either one function has a priority over the other. However a fixed priority ranking is often inconvenient since the priority varies according to the location of installation or to the user.